1. Field of the Invention
The present invention relates to a semiconductor integrated circuit, and more particularly to a semiconductor integrated circuit having a decoupling capacitor which reduces noise on a power supply wiring and a ground wiring formed on the semiconductor integrated circuit.
2. Description of the Prior Art
In order to reduce the effect of the noise on the power supply wiring in the semiconductor integrated circuit, there has been known a technique of coupling the power supply wiring and the ground wiring with a capacitor (decoupling capacitor). More specifically, a semiconductor integrated circuit is given a configuration in which along with the connection of a MOS capacitor formed on a semiconductor substrate, between the ground wiring and the power supply wiring, the ground wiring and the power supply wiring are disposed so as to be overlapped above and below with equal width with an interlayer insulating film in between, in order to further increase the degree of capacitive coupling between the ground wiring and the power supply wiring (see, Japanese Patent Applications Laid Open, No. 2001-15601 (prior art 1)).
Moreover, there has also been known a semiconductor integrated circuit in which shielding metal layers fixed to the ground potential level and a power supply voltage level, respectively, are formed between the semiconductor substrate and a signal wiring layer so as to cover almost the entire surface of the semiconductor substrate, to form a capacitor between the shielding metal layers by laminating the shielding metal layers via an insulating film (see, Japanese Patent Applications Laid Open, No. 2000-286385 (prior art 2)).
However, according to the invention described in the prior art 1, the power supply wiring and the ground wiring formed on the uppermost part of a multilayer wiring structure are connected to the substrate by contacts which penetrate the interlayer insulating films, so that the aspect ratio of the contact part becomes large and the inductance of the contact part is increased.
In particular, in the high frequency region, a residual inductance is elicited from the wiring together with the inductance of the contact part, and an LC serial resonance circuit is formed by these inductances and a coupling capacitor. As a result, there has been a problem in that the decoupling characteristics in the high frequency region is deteriorated due to reduction in the insertion loss caused by the occurrence of the resonance phenomenon in the high frequency region.
Moreover, since the thickness of the interlayer insulating film between the power supply wiring and the ground wiring is restrained by the process conditions of the multilayer wiring, there has been a problem in that the coupling capacitance cannot be increased and sufficient decoupling characteristics cannot be obtained.
Furthermore, when a multilayer wiring process is adopted in the invention described in the prior art 2, there are needed a large number of via holes for connecting signal wiring layers in the upper layers and the semiconductor substrate. However, the presence of the large number of via holes that penetrate shielding metal layers reduce the effect of the shielding metal layers for blocking the transmission of the noise from the semiconductor substrate to the signal wiring layers. Accordingly, there has been a problem in that application of the invention described in the prior art 2 to a multilayer wiring process is difficult.